Some video use cases may require extracting a part of a high resolution video. Such cases include, for example, zooming to a certain area in the video, following certain objects in the video or modifying or analyzing content in a limited area in a video sequence. The most straight-forward implementation of such use cases may involve decoding complete pictures and performing the desired operations on those. This kind of an approach results in high requirements on computational operations, increase in power consumption and slowdown in the processing.
Tiles in H.265/HEVC standard and slices in H.265/HEVC and H.264/AVC standards allow video encoders to create predefined picture areas that can be decoded independently from each other. The decoder may then select which tiles or slices it needs to decode in order to access the sample values of interest. A drawback of this approach is that the encoder needs to split the picture in a rigid grid of tiles or slices. The smaller the area of an individual tile or slice is, the more specific pixel areas can be decoded independently, but at the same time the coding efficiency is seriously degraded as the encoder cannot use the information from other slices or tiles to predict information in the current slice or tile. Another drawback is that a decoder needs to typically decode significant amount of pixels outside the actual area of interest as it needs to decode all the slices and tiles that intersect with the area of interest.